More of a what would you do I suppose.
My dd (10) has been in a weepy confessional mood recently and very worried about small things... Eg. months ago she "picked a skittle off the playground floor, brushed it clean and ate it"... Very concerned about germs suddenly and has she done the right thing. Part of me blames myself for this thinking maybe we have stressed her out telling her to wash her hands etc? (Of course hands have to be washed before meals etc.. I don't think we are over the top, but I don't understand why she is suddenly so worried about "bad things happening". I do remember going through a similar phase but think that I was older than 10).
Anyway, that's kind of a side issue. Some of her "confessions" concern time spent at a friend's house (also 10). One of these was when the friend gave her two vitamin tablets in water (but without saying they were vitamins, saying they were her Grandad's cancer medicine) and my daughter drank it. 3 months later she told me this story in tears (but did not seem remotely upset before that). So I cleared that one up with her friend's grandma (who is the main carer) who confirmed that they had been vitamins.
Another issue was the same friend asking my dd to drink some of a bath bomb they had just made. Apparently the friend drank some and my dd says she just licked a little bit of it and then rinsed her mouth out. Again this happened a while ago and again my daughter is in tears about it now. So I said that in future if she doesn't want to do something, just to say no etc... She obviously seems to have been easily lead which I would not have thought. Maybe now she will react in a different way to things she does not want to do.
Anyway, all this is fairly trivial I suppose. Now for the bombshell. At the same friend's house, and also a long time ago (my dd says a year, don't know how exact that would be), the friend went on a website called omegle which I had never heard of, to have completely inappropriate chats with strangers at the other end. My daughter in tears again saying it was nasty stuff. I asked her to give me some examples, which she didn't want to at first, but when she did, I agree that it was nasty 
.
So I told her how inappropriate this was for all the different reasons, and the dangers involved. And that (again) she has to stand up for what she knows is right and go and tell the adult present if something is wrong (friend's grandma was downstairs at the time). She says there were two playdates where her friend was on this website and that it hasn't happened for a long time.
My dilemma is how I broach this subject with the grandma without her feeling defensive and judged? She may well know, but maybe she doesn't? Just having the vitamin conversation with her you could see that she was slightly defensive, how defensive is she going to feel about this?
I think I do have to say something for her grandaughter's sake, but how do I phrase it?
Am also annoyed that my daughter was exposed to this, but that would not be part of my conversation with my friend (the grandma).